The invention relates to an electron cyclotron resonance plasma chemical vapor deposition apparatus (hereinafter referred to as ECR plasma CVD apparatus) suitable for forming a protective membrane or layer for, for example a magnetic disc of a hard disc recording apparatus.
It has been known that a fine and uniform protective membrane, i.e. film or layer, can be obtained through combined use of an ECR plasma CVD technique and an RF base plate bias system, and the technique has been used for forming a protective membrane in a post process in manufacturing a magnetic head. In case a magnetic disc for a hard disc recording device is formed of an aluminum disc, the RF base plate bias system is employed in the ECR plasma CVD apparatus in its post process, as well, so that a high quality protective membrane or layer can be formed. In this case, in order to form the membranes on both surfaces of a base plate or substrate at the same time regardless of a shape of a base plate holder, i.e. claws, it is suitable to adopt a system where a pulse-superposed DC bias is applied to the base plate.
However, in the conventional ECR plasma CVD apparatus having the bias application system, there has been a problem that the membrane can not be formed on a non-conductive glass base plate. In other words, in the recent magnetic disc market, since a higher density is required, glass is used as the base plate material. However, the glass base plate can not cope with this situation.
More specifically, since the glass base plate is non-conductive, DC bias can not be applied thereto. Further, in case of a base plate holder having a craw structure used for preventing damage or contamination which may occur on the base plate surface, since a bias distribution greatly depends on the claw structure of the base plate holder, a uniform membrane or layer is not obtained. Thus, the RF bias can not be employed either. It is considered that the bias need not be applied to the base plate at all, but the obtained membrane is not a fine membrane, so that it is not suitable as the protective membrane.
The present invention has been made in view of the above problems of the conventional ECR plasma CVD apparatus, and an object of the invention is to provide an ECR plasma CVD apparatus, wherein a uniform membrane can be formed on a non-conductive base plate or substrate, such as a glass base plate.
Further objects and advantages of the invention will be apparent from the following description of the invention.